1. Field of the Invention
This invention relates to equipment for scientific research, and lens fluorescence microscopes in particular, that are used for obtaining images of fluorescent objects immobilized on a glass. This invention also relates to a computerized fluorescent-microscopically method of reconstructing images of objects with resolution up to several nanometers (nm).
2. Discussion of Related Art
There are known optical microscopes which can create zoomed images of an object with object lenses that can show two spots on an object separately only when the distance between them is more than so called diffraction limit. This limit can be calculated using following formula: r=0.61λ/A (1), where λ is light wavelength for light collected by object lens with aperture A=n*sin(φ), n is a refraction index of substance which surrounds object spots, φ is an angle between object lens axis and extreme rays which fall into object lens and are detected in detector. Now, different types of devices are used for fluorescent microscopy by object lenses. Powerful arc-lamps, incandescent lamps, laser or sun light can be light sources for the microscope. Fluorescence starts in all dye molecules are present in a lighted area. The area is lighted through the object lens using a light-dividing dichroic mirror that lets exciting light to fall on the object and reflects fluorescence light to the detector. The second type of lighting occurs by sending laser light from the side and lights the object all the way down or through an object glass at a total internal reflection angle. In this case, light reaches a depth of only 0.3 of light wavelength from border between glass and an object which has a refraction index lower than glass. Object fluorescent light is collected by an object lens and sends an object image for visual observation and registration by a photomultiplier, a photographic tape or a digital video-camera. The main disadvantage of all existing lens microscopes is that they have a limit of resolution for two neighboring spots and the limit can be calculated according to the above formula (1).
Recently, microscopy using super lenses made from silver film has been developed. A film thickness less than 50 nm can assure resolution of two spots on a distance of approximately 50 nm from each other. (N. Fang and X. Zhang, Imaging properties of a metamaterial superlens, 2003, App phys Let v. 82, 2, 161-163; Nicholas Fang, Zhaowei Liu, Ta-Jen Yen, and Xiang Zhang Regenerating evanescent waves from a silver superlens, 2003, OPTICS EXPRESS, VoI. 11, No. 7, 682-687). Use of such microscopes on biological objects is unclear. The present microscope model has a resolution several times lower than a resolution of the device that we propose.
There are devices with a maximum resolution better than 1 nm, for example, electronic, tunnel, and atomic-force microscopes that have not only real advantages but also serious disadvantages, such as: complexity and expensiveness of their design and work with objects; lack of opportunity to receive a color image for distinguishing molecules of different types; objects that usually should be dried and treated with substances which change the mutual layout of different parts of the object. Atomic and tunnel microscopes also do not detect structures inside the object; only one spot can be detected at a time and a scanning speed does not overcome 1 square micron per min; and an end of the needle easily becomes dirty and does not then reach an object surface.
There is also a device, where object fluorescence is excited by laser through a pinhole on the tip of a glass fiber. The fiber is moved by drives in three directions to position an end of the fiber near light-reflecting, light-diffusing or covered with fluorescent molecules surface. This type of microscope does not use lenses and permits obtaining images with resolution ten times better than the resolution of common optical microscopes. These results can be reached only when the pinhole on the tip of glass fiber is much less in diameter than in light wavelength. The light comes onto an object with a depth much shorter than a light wavelength. Practically all light returns back into the glass fiber, except that part which was captured by objects from outside of the hole. Fluorescence, light-diffusion, and reflected light strength, captured in the object near the hole, are measured by a photomultiplier. The image of an object surface is reconstructed by a computer, which gathers information about the strength of measured light and data on an end of glass fiber coordinates. The main disadvantages of this system are: a need to use expensive high-precision and fast-acting mechanic units, responsible for moving of glass fiber against object; production of glass fiber with an end hole less than 50 nm in diameter is very expensive, complex and difficult for duplicating; the hole is easily dirtied and is not able to then reach an object surface; only an insignificant part of light can leave the fiber through the hole with a diameter less than light wavelength; increases of light intensity leads to overheating and destruction of the fiber end; it is impossible to detect fluorescence in the areas of the object which are not accessible by glass fiber; and only one spot can be detected at a time, and surface scanning speed does not exceed 1 square micron per minute.
One more new microscope type scans an object surface with several light beams simultaneously. National Institute of Standards and Technology (NIST) issued a grant for 5 years research work on creation of this microscope (http://www.betterhumans.com/News/news.aspx?articleID=2005-02-11-4, “Optical Microscopes Enter the Nano Age. Hybrid system being developed to image and measure features smaller than the wavelength of visible light”.) The article states that a 40 nm nanoparticle can be distinguished using this method. There are no indications of authors being successful in distinguishing two separate particles located on a distance less than 40 nm from each other. It is not clear from presented drawings and explanations how this method will allow distinguishing two particles on distance less than r<0.61λ/A between them and the suggested device will likely not reach resolution of object details, located on a distance much shorter than light wavelength.
One method of using common fluorescent microscope (Erwen, A Sharonov, J H Ferris, R M Hochstrasser: Direct visualization of nanopatterns by single-molecule imaging. App Phys Let 2005, 86: 043102) can be thought of as relevant to this invention. The main idea of this method is that a sample, a light film of polymer with free open spherical cells 1 micron in diameter, is dyed with very low concentration of fluorescent peptide. Such concentration allows to observe separate peptide molecules which can migrate in Brownian motion inside the hollow of spheres. The sample is lighted through an object glass by a laser beam. A lightning angle is equal to a total internal reflection angle. A laser beam excites fluorescence in a 150-200 micron layer of the sample near the glass. A location of several tens of molecules of fluorescing peptide, each of which was dyed by simultaneously fluorescing molecules, was detected by a high-sensitivity video camera (Roper Scientific, Cascade 512F with electrons multiplier built in CCD) in 500 sequential frames. Each frame was recorded to computer memory. Each image contained many spots of approximately 0.5 microns in diameter multiplied on a system zoom value. All these images were added to each other and a resultant image had a resolution not exceeding a resolution of a common fluorescent microscope. Main disadvantages of this system are: there is no information in the article about opportunity to calculate a location of detected spot centers and to generate an image on the basis of these spots with resolution higher than a diffraction limit (see formula 1); approaches to selective dyeing of object structures are not described in the article; and there is no description of solving that after dyeing, substances lose color in the process of detecting non fluorescing peptide molecules staying in an observation area. This will make the solution more thick and will not allow replacing such molecules with new fluorescing ones. This does not allow obtaining larger quantity of frames than 500. These large quantities are needed to receive image with resolution higher than allowed by a diffraction limit (see formula 1).